What describes the formation of the outer Jovian planets?

• A. Direct collapse of a single gas cloud
• B. Gravitational capture of distant planets
• C. Formed from ring debris
• D. Planetesimals of rock and ice attracting hydrogen and helium gas from the solar nebula

Answer: (B)

The formation of the outer Jovian planets is best explained by the core accretion model. In the young solar system, solid bodies in the protoplanetary disk collide and stick together, growing from small planetesimals into a substantial rocky/icy core. In the outer regions where ices are abundant, this core can grow to enough mass to become gravitationally dominant. Once a critical core mass is reached, the planet rapidly accretes a vast envelope of hydrogen and helium from the surrounding solar nebula, forming a massive gas giant with a thick gaseous envelope. This two-stage process—build a solid core, then pull in lots of gas—accounts for their large sizes and hydrogen/helium-rich compositions and fits what we observe about their orbits and formation environment.

Direct collapse of a single gas cloud would produce a star, not a planet. Forming from ring debris describes how moons can form from circumplanetary material, not how planets themselves form. Gravitational capture of distant planets could occur in some scenarios but is not the standard mechanism that explains the common, orderly giant-planet systems we see in our solar system.